# Buffer

<!--introduced_in=v0.1.90-->

> Stability: 2 - Stable

<!-- source_link=lib/buffer.js -->

`Buffer` objects are used to represent a fixed-length sequence of bytes. Many
Node.js APIs support `Buffer`s.

The `Buffer` class is a subclass of JavaScript's [`Uint8Array`][] class and
extends it with methods that cover additional use cases. Node.js APIs accept
plain [`Uint8Array`][]s wherever `Buffer`s are supported as well.

The `Buffer` class is within the global scope, making it unlikely that one
would need to ever use `require('buffer').Buffer`.

```js
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);

// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);

// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);

// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);

// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);

// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');

// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
```

## Buffers and character encodings
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    pr-url: https://github.com/nodejs/node/pull/7111
    description: Introduced `latin1` as an alias for `binary`.
  - version: v5.0.0
    pr-url: https://github.com/nodejs/node/pull/2859
    description: Removed the deprecated `raw` and `raws` encodings.
-->

When converting between `Buffer`s and strings, a character encoding may be
specified. If no character encoding is specified, UTF-8 will be used as the
default.

```js
const buf = Buffer.from('hello world', 'utf8');

console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=

console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
```

The character encodings currently supported by Node.js are the following:

* `'utf8'`: Multi-byte encoded Unicode characters. Many web pages and other
  document formats use [UTF-8][]. This is the default character encoding.
  When decoding a `Buffer` into a string that does not exclusively contain
  valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be used
  to represent those errors.

* `'utf16le'`: Multi-byte encoded Unicode characters. Unlike `'utf8'`, each
  character in the string will be encoded using either 2 or 4 bytes.
  Node.js only supports the [little-endian][endianness] variant of [UTF-16][].

* `'latin1'`: Latin-1 stands for [ISO-8859-1][]. This character encoding only
  supports the Unicode characters from `U+0000` to `U+00FF`. Each character is
  encoded using a single byte. Characters that do not fit into that range are
  truncated and will be mapped to characters in that range.

Converting a `Buffer` into a string using one of the above is referred to as
decoding, and converting a string into a `Buffer` is referred to as encoding.

Node.js also supports the following two binary-to-text encodings. For
binary-to-text encodings, the naming convention is reversed: Converting a
`Buffer` into a string is typically referred to as encoding, and converting a
string into a `Buffer` as decoding.

* `'base64'`: [Base64][] encoding. When creating a `Buffer` from a string,
  this encoding will also correctly accept "URL and Filename Safe Alphabet" as
  specified in [RFC 4648, Section 5][]. Whitespace characters such as spaces,
  tabs, and new lines contained within the base64-encoded string are ignored.

* `'hex'`: Encode each byte as two hexadecimal characters. Data truncation
  may occur when decoding string that do exclusively contain valid hexadecimal
  characters. See below for an example.

The following legacy character encodings are also supported:

* `'ascii'`: For 7-bit [ASCII][] data only. When encoding a string into a
  `Buffer`, this is equivalent to using `'latin1'`. When decoding a `Buffer`
  into a string, using encoding this will additionally unset the highest bit of
  each byte before decoding as `'latin1'`.
  Generally, there should be no reason to use this encoding, as `'utf8'`
  (or, if the data is known to always be ASCII-only, `'latin1'`) will be a
  better choice when encoding or decoding ASCII-only text. It is only provided
  for legacy compatibility.

* `'binary'`: Alias for `'latin1'`. See [binary strings][] for more background
  on this topic. The name of this encoding can be very misleading, as all of the
  encodings listed here convert between strings and binary data. For converting
  between strings and `Buffer`s, typically `'utf-8'` is the right choice.

* `'ucs2'`: Alias of `'utf16le'`. UCS-2 used to refer to a variant of UTF-16
  that did not support characters that had code points larger than U+FFFF.
  In Node.js, these code points are always supported.

```js
Buffer.from('1ag', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.

Buffer.from('1a7g', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').

Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
```

Modern Web browsers follow the [WHATWG Encoding Standard][] which aliases
both `'latin1'` and `'ISO-8859-1'` to `'win-1252'`. This means that while doing
something like `http.get()`, if the returned charset is one of those listed in
the WHATWG specification it is possible that the server actually returned
`'win-1252'`-encoded data, and using `'latin1'` encoding may incorrectly decode
the characters.

## Buffers and TypedArrays
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`Buffer` instances are also JavaScript [`Uint8Array`][] and [`TypedArray`][]
instances. All [`TypedArray`][] methods are available on `Buffer`s. There are,
however, subtle incompatibilities between the `Buffer` API and the
[`TypedArray`][] API.

In particular:

* While [`TypedArray#slice()`][] creates a copy of part of the `TypedArray`,
  [`Buffer#slice()`][`buf.slice()`] creates a view over the existing `Buffer`
  without copying. This behavior can be surprising, and only exists for legacy
  compatibility. [`TypedArray#subarray()`][] can be used to achieve the behavior
  of [`Buffer#slice()`][`buf.slice()`] on both `Buffer`s and other
  `TypedArray`s.
* [`buf.toString()`][] is incompatible with its `TypedArray` equivalent.
* A number of methods, e.g. [`buf.indexOf()`][], support additional arguments.

There are two ways to create new [`TypedArray`][] instances from a `Buffer`:

* Passing a `Buffer` to a [`TypedArray`][] constructor will copy the `Buffer`s
  contents, interpreted an array array of integers, and not as a byte sequence
  of the target type.

```js
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);

console.log(uint32array);

// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
```

* Passing the `Buffer`s underlying [`ArrayBuffer`][] will create a
  [`TypedArray`][] that shares its memory with the `Buffer`.

```js
const buf = Buffer.from('hello', 'utf16le');
const uint16arr = new Uint16Array(
  buf.buffer,
  buf.byteOffset,
  buf.length / Uint16Array.BYTES_PER_ELEMENT);

console.log(uint16array);

// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
```

It is possible to create a new `Buffer` that shares the same allocated
memory as a [`TypedArray`][] instance by using the `TypedArray` object’s
`.buffer` property in the same way. [`Buffer.from()`][`Buffer.from(arrayBuf)`]
behaves like `new Uint8Array()` in this context.

```js
const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);

// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>

arr[1] = 6000;

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
```

When creating a `Buffer` using a [`TypedArray`][]'s `.buffer`, it is
possible to use only a portion of the underlying [`ArrayBuffer`][] by passing in
`byteOffset` and `length` parameters.

```js
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);

console.log(buf.length);
// Prints: 16
```

The `Buffer.from()` and [`TypedArray.from()`][] have different signatures and
implementations. Specifically, the [`TypedArray`][] variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:

* `TypedArray.from(source[, mapFn[, thisArg]])`

The `Buffer.from()` method, however, does not support the use of a mapping
function:

* [`Buffer.from(array)`][]
* [`Buffer.from(buffer)`][]
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`]
* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`]

## Buffers and iteration

`Buffer` instances can be iterated over using `for..of` syntax:

```js
const buf = Buffer.from([1, 2, 3]);

for (const b of buf) {
  console.log(b);
}
// Prints:
//   1
//   2
//   3
```

Additionally, the [`buf.values()`][], [`buf.keys()`][], and
[`buf.entries()`][] methods can be used to create iterators.

## Class: `Buffer`

The `Buffer` class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.

### Static method: `Buffer.alloc(size[, fill[, encoding]])`
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                 buffer triggers a thrown exception.
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    description: Specifying an invalid string for `fill` triggers a thrown
                 exception.
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    description: Specifying an invalid string for `fill` now results in a
                 zero-filled buffer.
-->

* `size` {integer} The desired length of the new `Buffer`.
* `fill` {string|Buffer|Uint8Array|integer} A value to pre-fill the new `Buffer`
  with. **Default:** `0`.
* `encoding` {string} If `fill` is a string, this is its encoding.
  **Default:** `'utf8'`.

Allocates a new `Buffer` of `size` bytes. If `fill` is `undefined`, the
`Buffer` will be zero-filled.

```js
const buf = Buffer.alloc(5);

console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
```

If `size` is larger than
[`buffer.constants.MAX_LENGTH`][] or smaller than 0, [`ERR_INVALID_OPT_VALUE`][]
is thrown.

If `fill` is specified, the allocated `Buffer` will be initialized by calling
[`buf.fill(fill)`][`buf.fill()`].

```js
const buf = Buffer.alloc(5, 'a');

console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
```

If both `fill` and `encoding` are specified, the allocated `Buffer` will be
initialized by calling [`buf.fill(fill, encoding)`][`buf.fill()`].

```js
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');

console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
```

Calling [`Buffer.alloc()`][] can be measurably slower than the alternative
[`Buffer.allocUnsafe()`][] but ensures that the newly created `Buffer` instance
contents will never contain sensitive data from previous allocations, including
data that might not have been allocated for `Buffer`s.

A `TypeError` will be thrown if `size` is not a number.

### Static method: `Buffer.allocUnsafe(size)`
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* `size` {integer} The desired length of the new `Buffer`.

Allocates a new `Buffer` of `size` bytes. If `size` is larger than
[`buffer.constants.MAX_LENGTH`][] or smaller than 0, [`ERR_INVALID_OPT_VALUE`][]
is thrown.

The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`Buffer.alloc()`][] instead to initialize
`Buffer` instances with zeroes.

```js
const buf = Buffer.allocUnsafe(10);

console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>

buf.fill(0);

console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
```

A `TypeError` will be thrown if `size` is not a number.

The `Buffer` module pre-allocates an internal `Buffer` instance of
size [`Buffer.poolSize`][] that is used as a pool for the fast allocation of new
`Buffer` instances created using [`Buffer.allocUnsafe()`][],
[`Buffer.from(array)`][], and the deprecated `new Buffer(size)` constructor only
when `size` is less than or equal to `Buffer.poolSize >> 1` (floor of
[`Buffer.poolSize`][] divided by two).

Use of this pre-allocated internal memory pool is a key difference between
calling `Buffer.alloc(size, fill)` vs. `Buffer.allocUnsafe(size).fill(fill)`.
Specifically, `Buffer.alloc(size, fill)` will *never* use the internal `Buffer`
pool, while `Buffer.allocUnsafe(size).fill(fill)` *will* use the internal
`Buffer` pool if `size` is less than or equal to half [`Buffer.poolSize`][]. The
difference is subtle but can be important when an application requires the
additional performance that [`Buffer.allocUnsafe()`][] provides.

### Static method: `Buffer.allocUnsafeSlow(size)`
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* `size` {integer} The desired length of the new `Buffer`.

Allocates a new `Buffer` of `size` bytes. If `size` is larger than
[`buffer.constants.MAX_LENGTH`][] or smaller than 0, [`ERR_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`buf.fill(0)`][`buf.fill()`] to initialize
such `Buffer` instances with zeroes.

When using [`Buffer.allocUnsafe()`][] to allocate new `Buffer` instances,
allocations under 4KB are sliced from a single pre-allocated `Buffer`. This
allows applications to avoid the garbage collection overhead of creating many
individually allocated `Buffer` instances. This approach improves both
performance and memory usage by eliminating the need to track and clean up as
many individual `ArrayBuffer` objects.

However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled `Buffer` instance using `Buffer.allocUnsafeSlow()` and
then copying out the relevant bits.

```js
// Need to keep around a few small chunks of memory.
const store = [];

socket.on('readable', () => {
  let data;
  while (null !== (data = readable.read())) {
    // Allocate for retained data.
    const sb = Buffer.allocUnsafeSlow(10);

    // Copy the data into the new allocation.
    data.copy(sb, 0, 0, 10);

    store.push(sb);
  }
});
```

A `TypeError` will be thrown if `size` is not a number.

### Static method: `Buffer.byteLength(string[, encoding])`
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* `string` {string|Buffer|TypedArray|DataView|ArrayBuffer|SharedArrayBuffer} A
  value to calculate the length of.
* `encoding` {string} If `string` is a string, this is its encoding.
  **Default:** `'utf8'`.
* Returns: {integer} The number of bytes contained within `string`.

Returns the byte length of a string when encoded using `encoding`.
This is not the same as [`String.prototype.length`][], which does not account
for the encoding that is used to convert the string into bytes.

For `'base64'` and `'hex'`, this function assumes valid input. For strings that
contain non-base64/hex-encoded data (e.g. whitespace), the return value might be
greater than the length of a `Buffer` created from the string.

```js
const str = '\u00bd + \u00bc = \u00be';

console.log(`${str}: ${str.length} characters, ` +
            `${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
```

When `string` is a `Buffer`/[`DataView`][]/[`TypedArray`][]/[`ArrayBuffer`][]/
[`SharedArrayBuffer`][], the byte length as reported by `.byteLength`
is returned.

### Static method: `Buffer.compare(buf1, buf2)`
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* `buf1` {Buffer|Uint8Array}
* `buf2` {Buffer|Uint8Array}
* Returns: {integer} Either `-1`, `0`, or `1`, depending on the result of the
  comparison. See [`buf.compare()`][] for details.

Compares `buf1` to `buf2`, typically for the purpose of sorting arrays of
`Buffer` instances. This is equivalent to calling
[`buf1.compare(buf2)`][`buf.compare()`].

```js
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];

console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
```

### Static method: `Buffer.concat(list[, totalLength])`
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* `list` {Buffer[] | Uint8Array[]} List of `Buffer` or [`Uint8Array`][]
  instances to concatenate.
* `totalLength` {integer} Total length of the `Buffer` instances in `list`
  when concatenated.
* Returns: {Buffer}

Returns a new `Buffer` which is the result of concatenating all the `Buffer`
instances in the `list` together.

If the list has no items, or if the `totalLength` is 0, then a new zero-length
`Buffer` is returned.

If `totalLength` is not provided, it is calculated from the `Buffer` instances
in `list` by adding their lengths.

If `totalLength` is provided, it is coerced to an unsigned integer. If the
combined length of the `Buffer`s in `list` exceeds `totalLength`, the result is
truncated to `totalLength`.

```js
// Create a single `Buffer` from a list of three `Buffer` instances.

const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;

console.log(totalLength);
// Prints: 42

const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);

console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
```

### Static method: `Buffer.from(array)`
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* `array` {integer[]}

Allocates a new `Buffer` using an `array` of bytes in the range `0` – `255`.
Array entries outside that range will be truncated to fit into it.

```js
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'.
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
```

A `TypeError` will be thrown if `array` is not an `Array` or another type
appropriate for `Buffer.from()` variants.

`Buffer.from(array)` and [`Buffer.from(string)`][] may also use the internal
`Buffer` pool like [`Buffer.allocUnsafe()`][] does.

### Static method: `Buffer.from(arrayBuffer[, byteOffset[, length]])`
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* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`][],
  [`SharedArrayBuffer`][], for example the `.buffer` property of a
  [`TypedArray`][].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`.
* `length` {integer} Number of bytes to expose.
  **Default:** `arrayBuffer.byteLength - byteOffset`.

This creates a view of the [`ArrayBuffer`][] without copying the underlying
memory. For example, when passed a reference to the `.buffer` property of a
[`TypedArray`][] instance, the newly created `Buffer` will share the same
allocated memory as the [`TypedArray`][].

```js
const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;

// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);

console.log(buf);
// Prints: <Buffer 88 13 a0 0f>

// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;

console.log(buf);
// Prints: <Buffer 88 13 70 17>
```

The optional `byteOffset` and `length` arguments specify a memory range within
the `arrayBuffer` that will be shared by the `Buffer`.

```js
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
// Prints: 2
```

A `TypeError` will be thrown if `arrayBuffer` is not an [`ArrayBuffer`][] or a
[`SharedArrayBuffer`][] or another type appropriate for `Buffer.from()`
variants.

### Static method: `Buffer.from(buffer)`
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* `buffer` {Buffer|Uint8Array} An existing `Buffer` or [`Uint8Array`][] from
  which to copy data.

Copies the passed `buffer` data onto a new `Buffer` instance.

```js
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);

buf1[0] = 0x61;

console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
```

A `TypeError` will be thrown if `buffer` is not a `Buffer` or another type
appropriate for `Buffer.from()` variants.

### Static method: `Buffer.from(object[, offsetOrEncoding[, length]])`
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* `object` {Object} An object supporting `Symbol.toPrimitive` or `valueOf()`.
* `offsetOrEncoding` {integer|string} A byte-offset or encoding.
* `length` {integer} A length.

For objects whose `valueOf()` function returns a value not strictly equal to
`object`, returns `Buffer.from(object.valueOf(), offsetOrEncoding, length)`.

```js
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```

For objects that support `Symbol.toPrimitive`, returns
`Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)`.

```js
class Foo {
  [Symbol.toPrimitive]() {
    return 'this is a test';
  }
}

const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```

A `TypeError` will be thrown if `object` does not have the mentioned methods or
is not of another type appropriate for `Buffer.from()` variants.

### Static method: `Buffer.from(string[, encoding])`
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* `string` {string} A string to encode.
* `encoding` {string} The encoding of `string`. **Default:** `'utf8'`.

Creates a new `Buffer` containing `string`. The `encoding` parameter identifies
the character encoding to be used when converting `string` into bytes.

```js
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');

console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tÃ©st
```

A `TypeError` will be thrown if `string` is not a string or another type
appropriate for `Buffer.from()` variants.

### Static method: `Buffer.isBuffer(obj)`
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* `obj` {Object}
* Returns: {boolean}

Returns `true` if `obj` is a `Buffer`, `false` otherwise.

### Static method: `Buffer.isEncoding(encoding)`
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* `encoding` {string} A character encoding name to check.
* Returns: {boolean}

Returns `true` if `encoding` is the name of a supported character encoding,
or `false` otherwise.

```js
console.log(Buffer.isEncoding('utf-8'));
// Prints: true

console.log(Buffer.isEncoding('hex'));
// Prints: true

console.log(Buffer.isEncoding('utf/8'));
// Prints: false

console.log(Buffer.isEncoding(''));
// Prints: false
```

### Class Property: `Buffer.poolSize`
<!-- YAML
added: v0.11.3
-->

* {integer} **Default:** `8192`

This is the size (in bytes) of pre-allocated internal `Buffer` instances used
for pooling. This value may be modified.

### `buf[index]`
<!-- YAML
type: property
name: [index]
-->

* `index` {integer}

The index operator `[index]` can be used to get and set the octet at position
`index` in `buf`. The values refer to individual bytes, so the legal value
range is between `0x00` and `0xFF` (hex) or `0` and `255` (decimal).

This operator is inherited from `Uint8Array`, so its behavior on out-of-bounds
access is the same as `Uint8Array`. In other words, `buf[index]` returns
`undefined` when `index` is negative or greater or equal to `buf.length`, and
`buf[index] = value` does not modify the buffer if `index` is negative or
`>= buf.length`.

```js
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)

const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);

for (let i = 0; i < str.length; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf.toString('utf8'));
// Prints: Node.js
```

### `buf.buffer`

* {ArrayBuffer} The underlying `ArrayBuffer` object based on which this `Buffer`
  object is created.

This `ArrayBuffer` is not guaranteed to correspond exactly to the original
`Buffer`. See the notes on `buf.byteOffset` for details.

```js
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);

console.log(buffer.buffer === arrayBuffer);
// Prints: true
```

### `buf.byteOffset`

* {integer} The `byteOffset` of the `Buffer`s underlying `ArrayBuffer` object.

When setting `byteOffset` in `Buffer.from(ArrayBuffer, byteOffset, length)`,
or sometimes when allocating a `Buffer` smaller than `Buffer.poolSize`, the
buffer does not start from a zero offset on the underlying `ArrayBuffer`.

This can cause problems when accessing the underlying `ArrayBuffer` directly
using `buf.buffer`, as other parts of the `ArrayBuffer` may be unrelated
to the `Buffer` object itself.

A common issue when creating a `TypedArray` object that shares its memory with
a `Buffer` is that in this case one needs to specify the `byteOffset` correctly:

```js
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = new Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
```

### `buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])`
<!-- YAML
added: v0.11.13
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `target` parameter can now be a `Uint8Array`.
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5880
    description: Additional parameters for specifying offsets are supported now.
-->

* `target` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] with which to
  compare `buf`.
* `targetStart` {integer} The offset within `target` at which to begin
  comparison. **Default:** `0`.
* `targetEnd` {integer} The offset within `target` at which to end comparison
  (not inclusive). **Default:** `target.length`.
* `sourceStart` {integer} The offset within `buf` at which to begin comparison.
  **Default:** `0`.
* `sourceEnd` {integer} The offset within `buf` at which to end comparison
  (not inclusive). **Default:** [`buf.length`][].
* Returns: {integer}

Compares `buf` with `target` and returns a number indicating whether `buf`
comes before, after, or is the same as `target` in sort order.
Comparison is based on the actual sequence of bytes in each `Buffer`.

* `0` is returned if `target` is the same as `buf`
* `1` is returned if `target` should come *before* `buf` when sorted.
* `-1` is returned if `target` should come *after* `buf` when sorted.

```js
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');

console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
```

The optional `targetStart`, `targetEnd`, `sourceStart`, and `sourceEnd`
arguments can be used to limit the comparison to specific ranges within `target`
and `buf` respectively.

```js
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);

console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
```

[`ERR_OUT_OF_RANGE`][] is thrown if `targetStart < 0`, `sourceStart < 0`,
`targetEnd > target.byteLength`, or `sourceEnd > source.byteLength`.

### `buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])`
<!-- YAML
added: v0.1.90
-->

* `target` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] to copy into.
* `targetStart` {integer} The offset within `target` at which to begin
  writing. **Default:** `0`.
* `sourceStart` {integer} The offset within `buf` from which to begin copying.
  **Default:** `0`.
* `sourceEnd` {integer} The offset within `buf` at which to stop copying (not
  inclusive). **Default:** [`buf.length`][].
* Returns: {integer} The number of bytes copied.

Copies data from a region of `buf` to a region in `target`, even if the `target`
memory region overlaps with `buf`.

[`TypedArray#set()`][] performs the same operation, and is available for all
TypedArrays, including Node.js `Buffer`s, although it takes different
function arguments.

```js
// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);

console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
```

```js
// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.

const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf[i] = i + 97;
}

buf.copy(buf, 0, 4, 10);

console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
```

### `buf.entries()`
<!-- YAML
added: v1.1.0
-->

* Returns: {Iterator}

Creates and returns an [iterator][] of `[index, byte]` pairs from the contents
of `buf`.

```js
// Log the entire contents of a `Buffer`.

const buf = Buffer.from('buffer');

for (const pair of buf.entries()) {
  console.log(pair);
}
// Prints:
//   [0, 98]
//   [1, 117]
//   [2, 102]
//   [3, 102]
//   [4, 101]
//   [5, 114]
```

### `buf.equals(otherBuffer)`
<!-- YAML
added: v0.11.13
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The arguments can now be `Uint8Array`s.
-->

* `otherBuffer` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] with which to
  compare `buf`.
* Returns: {boolean}

Returns `true` if both `buf` and `otherBuffer` have exactly the same bytes,
`false` otherwise. Equivalent to
[`buf.compare(otherBuffer) === 0`][`buf.compare()`].

```js
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');

console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
```

### `buf.fill(value[, offset[, end]][, encoding])`
<!-- YAML
added: v0.5.0
changes:
  - version: v11.0.0
    pr-url: https://github.com/nodejs/node/pull/22969
    description: Throws `ERR_OUT_OF_RANGE` instead of `ERR_INDEX_OUT_OF_RANGE`.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18790
    description: Negative `end` values throw an `ERR_INDEX_OUT_OF_RANGE` error.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18129
    description: Attempting to fill a non-zero length buffer with a zero length
                 buffer triggers a thrown exception.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/17427
    description: Specifying an invalid string for `value` triggers a thrown
                 exception.
  - version: v5.7.0
    pr-url: https://github.com/nodejs/node/pull/4935
    description: The `encoding` parameter is supported now.
-->

* `value` {string|Buffer|Uint8Array|integer} The value with which to fill `buf`.
* `offset` {integer} Number of bytes to skip before starting to fill `buf`.
  **Default:** `0`.
* `end` {integer} Where to stop filling `buf` (not inclusive). **Default:**
  [`buf.length`][].
* `encoding` {string} The encoding for `value` if `value` is a string.
  **Default:** `'utf8'`.
* Returns: {Buffer} A reference to `buf`.

Fills `buf` with the specified `value`. If the `offset` and `end` are not given,
the entire `buf` will be filled:

```js
// Fill a `Buffer` with the ASCII character 'h'.

const b = Buffer.allocUnsafe(50).fill('h');

console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
```

`value` is coerced to a `uint32` value if it is not a string, `Buffer`, or
integer. If the resulting integer is greater than `255` (decimal), `buf` will be
filled with `value & 255`.

If the final write of a `fill()` operation falls on a multi-byte character,
then only the bytes of that character that fit into `buf` are written:

```js
// Fill a `Buffer` with character that takes up two bytes in UTF-8.

console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
```

If `value` contains invalid characters, it is truncated; if no valid
fill data remains, an exception is thrown:

```js
const buf = Buffer.allocUnsafe(5);

console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
```

### `buf.includes(value[, byteOffset][, encoding])`
<!-- YAML
added: v5.3.0
-->

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` {string} If `value` is a string, this is its encoding.
  **Default:** `'utf8'`.
* Returns: {boolean} `true` if `value` was found in `buf`, `false` otherwise.

Equivalent to [`buf.indexOf() !== -1`][`buf.indexOf()`].

```js
const buf = Buffer.from('this is a buffer');

console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
```

### `buf.indexOf(value[, byteOffset][, encoding])`
<!-- YAML
added: v1.5.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `value` can now be a `Uint8Array`.
  - version: v5.7.0, v4.4.0
    pr-url: https://github.com/nodejs/node/pull/4803
    description: When `encoding` is being passed, the `byteOffset` parameter
                 is no longer required.
-->

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` {string} If `value` is a string, this is the encoding used to
  determine the binary representation of the string that will be searched for in
  `buf`. **Default:** `'utf8'`.
* Returns: {integer} The index of the first occurrence of `value` in `buf`, or
  `-1` if `buf` does not contain `value`.

If `value` is:

* a string, `value` is interpreted according to the character encoding in
  `encoding`.
* a `Buffer` or [`Uint8Array`][], `value` will be used in its entirety.
  To compare a partial `Buffer`, use [`buf.slice()`][].
* a number, `value` will be interpreted as an unsigned 8-bit integer
  value between `0` and `255`.

```js
const buf = Buffer.from('this is a buffer');

console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8

const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');

console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
```

If `value` is not a string, number, or `Buffer`, this method will throw a
`TypeError`. If `value` is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.

If `byteOffset` is not a number, it will be coerced to a number. If the result
of coercion is `NaN` or `0`, then the entire buffer will be searched. This
behavior matches [`String#indexOf()`][].

```js
const b = Buffer.from('abcdef');

// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));

// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
```

If `value` is an empty string or empty `Buffer` and `byteOffset` is less
than `buf.length`, `byteOffset` will be returned. If `value` is empty and
`byteOffset` is at least `buf.length`, `buf.length` will be returned.

### `buf.keys()`
<!-- YAML
added: v1.1.0
-->

* Returns: {Iterator}

Creates and returns an [iterator][] of `buf` keys (indices).

```js
const buf = Buffer.from('buffer');

for (const key of buf.keys()) {
  console.log(key);
}
// Prints:
//   0
//   1
//   2
//   3
//   4
//   5
```

### `buf.lastIndexOf(value[, byteOffset][, encoding])`
<!-- YAML
added: v6.0.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `value` can now be a `Uint8Array`.
-->

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:**
  `buf.length - 1`.
* `encoding` {string} If `value` is a string, this is the encoding used to
  determine the binary representation of the string that will be searched for in
  `buf`. **Default:** `'utf8'`.
* Returns: {integer} The index of the last occurrence of `value` in `buf`, or
  `-1` if `buf` does not contain `value`.

Identical to [`buf.indexOf()`][], except the last occurrence of `value` is found
rather than the first occurrence.

```js
const buf = Buffer.from('this buffer is a buffer');

console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1

const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');

console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
```

If `value` is not a string, number, or `Buffer`, this method will throw a
`TypeError`. If `value` is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.

If `byteOffset` is not a number, it will be coerced to a number. Any arguments
that coerce to `NaN`, like `{}` or `undefined`, will search the whole buffer.
This behavior matches [`String#lastIndexOf()`][].

```js
const b = Buffer.from('abcdef');

// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));

// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));

// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
```

If `value` is an empty string or empty `Buffer`, `byteOffset` will be returned.

### `buf.length`
<!-- YAML
added: v0.1.90
-->

* {integer}

Returns the number of bytes in `buf`.

```js
// Create a `Buffer` and write a shorter string to it using UTF-8.

const buf = Buffer.alloc(1234);

console.log(buf.length);
// Prints: 1234

buf.write('some string', 0, 'utf8');

console.log(buf.length);
// Prints: 1234
```

### `buf.parent`
<!-- YAML
deprecated: v8.0.0
-->

> Stability: 0 - Deprecated: Use [`buf.buffer`][] instead.

The `buf.parent` property is a deprecated alias for `buf.buffer`.

### `buf.readBigInt64BE([offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

Reads a signed, big-endian 64-bit integer from `buf` at the specified `offset`.

Integers read from a `Buffer` are interpreted as two's complement signed
values.

### `buf.readBigInt64LE([offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

Reads a signed, little-endian 64-bit integer from `buf` at the specified
`offset`.

Integers read from a `Buffer` are interpreted as two's complement signed
values.

### `buf.readBigUInt64BE([offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

Reads an unsigned, big-endian 64-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);

console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
```

### `buf.readBigUInt64LE([offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

Reads an unsigned, little-endian 64-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);

console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
```

### `buf.readDoubleBE([offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {number}

Reads a 64-bit, big-endian double from `buf` at the specified `offset`.

```js
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);

console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
```

### `buf.readDoubleLE([offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {number}

Reads a 64-bit, little-endian double from `buf` at the specified `offset`.

```js
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);

console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readFloatBE([offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {number}

Reads a 32-bit, big-endian float from `buf` at the specified `offset`.

```js
const buf = Buffer.from([1, 2, 3, 4]);

console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
```

### `buf.readFloatLE([offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {number}

Reads a 32-bit, little-endian float from `buf` at the specified `offset`.

```js
const buf = Buffer.from([1, 2, 3, 4]);

console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readInt8([offset])`
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer}

Reads a signed 8-bit integer from `buf` at the specified `offset`.

Integers read from a `Buffer` are interpreted as two's complement signed values.

```js
const buf = Buffer.from([-1, 5]);

console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readInt16BE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

Reads a signed, big-endian 16-bit integer from `buf` at the specified `offset`.

Integers read from a `Buffer` are interpreted as two's complement signed values.

```js
const buf = Buffer.from([0, 5]);

console.log(buf.readInt16BE(0));
// Prints: 5
```

### `buf.readInt16LE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

Reads a signed, little-endian 16-bit integer from `buf` at the specified
`offset`.

Integers read from a `Buffer` are interpreted as two's complement signed values.

```js
const buf = Buffer.from([0, 5]);

console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readInt32BE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

Reads a signed, big-endian 32-bit integer from `buf` at the specified `offset`.

Integers read from a `Buffer` are interpreted as two's complement signed values.

```js
const buf = Buffer.from([0, 0, 0, 5]);

console.log(buf.readInt32BE(0));
// Prints: 5
```

### `buf.readInt32LE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

Reads a signed, little-endian 32-bit integer from `buf` at the specified
`offset`.

Integers read from a `Buffer` are interpreted as two's complement signed values.

```js
const buf = Buffer.from([0, 0, 0, 5]);

console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readIntBE(offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to read. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer}

Reads `byteLength` number of bytes from `buf` at the specified `offset`
and interprets the result as a big-endian, two's complement signed value
supporting up to 48 bits of accuracy.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readIntLE(offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to read. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer}

Reads `byteLength` number of bytes from `buf` at the specified `offset`
and interprets the result as a little-endian, two's complement signed value
supporting up to 48 bits of accuracy.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
```

### `buf.readUInt8([offset])`
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer}

Reads an unsigned 8-bit integer from `buf` at the specified `offset`.

```js
const buf = Buffer.from([1, -2]);

console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readUInt16BE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

Reads an unsigned, big-endian 16-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x12, 0x34, 0x56]);

console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
```

### `buf.readUInt16LE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

Reads an unsigned, little-endian 16-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x12, 0x34, 0x56]);

console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readUInt32BE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

Reads an unsigned, big-endian 32-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);

console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
```

### `buf.readUInt32LE([offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

Reads an unsigned, little-endian 32-bit integer from `buf` at the specified
`offset`.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);

console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readUIntBE(offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to read. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer}

Reads `byteLength` number of bytes from `buf` at the specified `offset`
and interprets the result as an unsigned big-endian integer supporting
up to 48 bits of accuracy.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readUIntLE(offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `offset` {integer} Number of bytes to skip before starting to read. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to read. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer}

Reads `byteLength` number of bytes from `buf` at the specified `offset`
and interprets the result as an unsigned, little-endian integer supporting
up to 48 bits of accuracy.

```js
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
```

### `buf.subarray([start[, end]])`
<!-- YAML
added: v3.0.0
-->

* `start` {integer} Where the new `Buffer` will start. **Default:** `0`.
* `end` {integer} Where the new `Buffer` will end (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {Buffer}

Returns a new `Buffer` that references the same memory as the original, but
offset and cropped by the `start` and `end` indices.

Specifying `end` greater than [`buf.length`][] will return the same result as
that of `end` equal to [`buf.length`][].

This method is inherited from [`TypedArray#subarray()`][].

Modifying the new `Buffer` slice will modify the memory in the original `Buffer`
because the allocated memory of the two objects overlap.

```js
// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.

const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

const buf2 = buf1.subarray(0, 3);

console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc

buf1[0] = 33;

console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
```

Specifying negative indexes causes the slice to be generated relative to the
end of `buf` rather than the beginning.

```js
const buf = Buffer.from('buffer');

console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)

console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)

console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
```

### `buf.slice([start[, end]])`
<!-- YAML
added: v0.3.0
changes:
  - version: v7.1.0, v6.9.2
    pr-url: https://github.com/nodejs/node/pull/9341
    description: Coercing the offsets to integers now handles values outside
                 the 32-bit integer range properly.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/9101
    description: All offsets are now coerced to integers before doing any
                 calculations with them.
-->

* `start` {integer} Where the new `Buffer` will start. **Default:** `0`.
* `end` {integer} Where the new `Buffer` will end (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {Buffer}

Returns a new `Buffer` that references the same memory as the original, but
offset and cropped by the `start` and `end` indices.

This is the same behavior as `buf.subarray()`.

This method is not compatible with the `Uint8Array.prototype.slice()`,
which is a superclass of `Buffer`. To copy the slice, use
`Uint8Array.prototype.slice()`.

```js
const buf = Buffer.from('buffer');

const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
// Prints: cuffer

console.log(buf.toString());
// Prints: buffer
```

### `buf.swap16()`
<!-- YAML
added: v5.10.0
-->

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of unsigned 16-bit integers and swaps the
byte order *in-place*. Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][]
is not a multiple of 2.

```js
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap16();

console.log(buf1);
// Prints: <Buffer 02 01 04 03 06 05 08 07>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap16();
// Throws ERR_INVALID_BUFFER_SIZE.
```

One convenient use of `buf.swap16()` is to perform a fast in-place conversion
between UTF-16 little-endian and UTF-16 big-endian:

```js
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); // Convert to big-endian UTF-16 text.
```

### `buf.swap32()`
<!-- YAML
added: v5.10.0
-->

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of unsigned 32-bit integers and swaps the
byte order *in-place*. Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][]
is not a multiple of 4.

```js
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap32();

console.log(buf1);
// Prints: <Buffer 04 03 02 01 08 07 06 05>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap32();
// Throws ERR_INVALID_BUFFER_SIZE.
```

### `buf.swap64()`
<!-- YAML
added: v6.3.0
-->

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of 64-bit numbers and swaps byte order *in-place*.
Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][] is not a multiple of 8.

```js
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap64();

console.log(buf1);
// Prints: <Buffer 08 07 06 05 04 03 02 01>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap64();
// Throws ERR_INVALID_BUFFER_SIZE.
```

### `buf.toJSON()`
<!-- YAML
added: v0.9.2
-->

* Returns: {Object}

Returns a JSON representation of `buf`. [`JSON.stringify()`][] implicitly calls
this function when stringifying a `Buffer` instance.

`Buffer.from()` accepts objects in the format returned from this method.
In particular, `Buffer.from(buf.toJSON())` works like `Buffer.from(buf)`.

```js
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);

console.log(json);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}

const copy = JSON.parse(json, (key, value) => {
  return value && value.type === 'Buffer' ?
    Buffer.from(value) :
    value;
});

console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
```

### `buf.toString([encoding[, start[, end]]])`
<!-- YAML
added: v0.1.90
-->

* `encoding` {string} The character encoding to use. **Default:** `'utf8'`.
* `start` {integer} The byte offset to start decoding at. **Default:** `0`.
* `end` {integer} The byte offset to stop decoding at (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {string}

Decodes `buf` to a string according to the specified character encoding in
`encoding`. `start` and `end` may be passed to decode only a subset of `buf`.

If `encoding` is `'utf8'` and a byte sequence in the input is not valid UTF-8,
then each invalid byte is replaced with the replacement character `U+FFFD`.

The maximum length of a string instance (in UTF-16 code units) is available
as [`buffer.constants.MAX_STRING_LENGTH`][].

```js
const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

console.log(buf1.toString('utf8'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('utf8', 0, 5));
// Prints: abcde

const buf2 = Buffer.from('tést');

console.log(buf2.toString('hex'));
// Prints: 74c3a97374
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
// Prints: té
```

### `buf.values()`
<!-- YAML
added: v1.1.0
-->

* Returns: {Iterator}

Creates and returns an [iterator][] for `buf` values (bytes). This function is
called automatically when a `Buffer` is used in a `for..of` statement.

```js
const buf = Buffer.from('buffer');

for (const value of buf.values()) {
  console.log(value);
}
// Prints:
//   98
//   117
//   102
//   102
//   101
//   114

for (const value of buf) {
  console.log(value);
}
// Prints:
//   98
//   117
//   102
//   102
//   101
//   114
```

### `buf.write(string[, offset[, length]][, encoding])`
<!-- YAML
added: v0.1.90
-->

* `string` {string} String to write to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write `string`.
  **Default:** `0`.
* `length` {integer} Maximum number of bytes to write (written bytes will not
  exceed `buf.length - offset`). **Default:** `buf.length - offset`.
* `encoding` {string} The character encoding of `string`. **Default:** `'utf8'`.
* Returns: {integer} Number of bytes written.

Writes `string` to `buf` at `offset` according to the character encoding in
`encoding`. The `length` parameter is the number of bytes to write. If `buf` did
not contain enough space to fit the entire string, only part of `string` will be
written. However, partially encoded characters will not be written.

```js
const buf = Buffer.alloc(256);

const len = buf.write('\u00bd + \u00bc = \u00be', 0);

console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾

const buffer = Buffer.alloc(10);

const length = buffer.write('abcd', 8);

console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
```

### `buf.writeBigInt64BE(value[, offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `value` {bigint} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian.

`value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
```

### `buf.writeBigInt64LE(value[, offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `value` {bigint} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian.

`value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
```

### `buf.writeBigUInt64BE(value[, offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `value` {bigint} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian.

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

console.log(buf);
// Prints: <Buffer de ca fa fe ca ce fa de>
```

### `buf.writeBigUInt64LE(value[, offset])`
<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

* `value` {bigint} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

console.log(buf);
// Prints: <Buffer de fa ce ca fe fa ca de>
```

### `buf.writeDoubleBE(value[, offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian. The `value`
must be a JavaScript number. Behavior is undefined when `value` is anything
other than a JavaScript number.

```js
const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
```

### `buf.writeDoubleLE(value[, offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian. The `value`
must be a JavaScript number. Behavior is undefined when `value` is anything
other than a JavaScript number.

```js
const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
```

### `buf.writeFloatBE(value[, offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian. Behavior is
undefined when `value` is anything other than a JavaScript number.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer 4f 4a fe bb>

```

### `buf.writeFloatLE(value[, offset])`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian. Behavior is
undefined when `value` is anything other than a JavaScript number.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
```

### `buf.writeInt8(value[, offset])`
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset`. `value` must be a valid
signed 8-bit integer. Behavior is undefined when `value` is anything other than
a signed 8-bit integer.

`value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(2);

buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);

console.log(buf);
// Prints: <Buffer 02 fe>
```

### `buf.writeInt16BE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian.  The `value`
must be a valid signed 16-bit integer. Behavior is undefined when `value` is
anything other than a signed 16-bit integer.

The `value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
// Prints: <Buffer 01 02>
```

### `buf.writeInt16LE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian.  The `value`
must be a valid signed 16-bit integer. Behavior is undefined when `value` is
anything other than a signed 16-bit integer.

The `value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
// Prints: <Buffer 04 03>
```

### `buf.writeInt32BE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian. The `value`
must be a valid signed 32-bit integer. Behavior is undefined when `value` is
anything other than a signed 32-bit integer.

The `value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04>
```

### `buf.writeInt32LE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian. The `value`
must be a valid signed 32-bit integer. Behavior is undefined when `value` is
anything other than a signed 32-bit integer.

The `value` is interpreted and written as a two's complement signed integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05>
```

### `buf.writeIntBE(value, offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to write. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `byteLength` bytes of `value` to `buf` at the specified `offset`
as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when
`value` is anything other than a signed integer.

```js
const buf = Buffer.allocUnsafe(6);

buf.writeIntBE(0x1234567890ab, 0, 6);

console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>

```

### `buf.writeIntLE(value, offset, byteLength)`
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to write. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `byteLength` bytes of `value` to `buf` at the specified `offset`
as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when `value` is anything other than a signed integer.

```js
const buf = Buffer.allocUnsafe(6);

buf.writeIntLE(0x1234567890ab, 0, 6);

console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```

### `buf.writeUInt8(value[, offset])`
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset`. `value` must be a
valid unsigned 8-bit integer. Behavior is undefined when `value` is anything
other than an unsigned 8-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);

console.log(buf);
// Prints: <Buffer 03 04 23 42>
```

### `buf.writeUInt16BE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian. The `value`
must be a valid unsigned 16-bit integer. Behavior is undefined when `value`
is anything other than an unsigned 16-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);

console.log(buf);
// Prints: <Buffer de ad be ef>
```

### `buf.writeUInt16LE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian. The `value`
must be a valid unsigned 16-bit integer. Behavior is undefined when `value` is
anything other than an unsigned 16-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);

console.log(buf);
// Prints: <Buffer ad de ef be>
```

### `buf.writeUInt32BE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as big-endian. The `value`
must be a valid unsigned 32-bit integer. Behavior is undefined when `value`
is anything other than an unsigned 32-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);
// Prints: <Buffer fe ed fa ce>
```

### `buf.writeUInt32LE(value[, offset])`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `value` to `buf` at the specified `offset` as little-endian. The `value`
must be a valid unsigned 32-bit integer. Behavior is undefined when `value` is
anything other than an unsigned 32-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);
// Prints: <Buffer ce fa ed fe>
```

### `buf.writeUIntBE(value, offset, byteLength)`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to write. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `byteLength` bytes of `value` to `buf` at the specified `offset`
as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when `value` is anything other than an unsigned integer.

```js
const buf = Buffer.allocUnsafe(6);

buf.writeUIntBE(0x1234567890ab, 0, 6);

console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
```

### `buf.writeUIntLE(value, offset, byteLength)`
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
  satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to write. Must satisfy
  `0 < byteLength <= 6`.
* Returns: {integer} `offset` plus the number of bytes written.

Writes `byteLength` bytes of `value` to `buf` at the specified `offset`
as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when `value` is anything other than an unsigned integer.

```js
const buf = Buffer.allocUnsafe(6);

buf.writeUIntLE(0x1234567890ab, 0, 6);

console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
```

### `new Buffer(array)`
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

> Stability: 0 - Deprecated: Use [`Buffer.from(array)`][] instead.

* `array` {integer[]} An array of bytes to copy from.

See [`Buffer.from(array)`][].

### `new Buffer(arrayBuffer[, byteOffset[, length]])`
<!-- YAML
added: v3.0.0
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
  - version: v6.0.0
    pr-url: https://github.com/nodejs/node/pull/4682
    description: The `byteOffset` and `length` parameters are supported now.
-->

> Stability: 0 - Deprecated: Use
> [`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`]
> instead.

* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`][],
  [`SharedArrayBuffer`][] or the `.buffer` property of a [`TypedArray`][].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`.
* `length` {integer} Number of bytes to expose.
  **Default:** `arrayBuffer.byteLength - byteOffset`.

See
[`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`].

### `new Buffer(buffer)`
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

> Stability: 0 - Deprecated: Use [`Buffer.from(buffer)`][] instead.

* `buffer` {Buffer|Uint8Array} An existing `Buffer` or [`Uint8Array`][] from
  which to copy data.

See [`Buffer.from(buffer)`][].

### `new Buffer(size)`
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/12141
    description: The `new Buffer(size)` will return zero-filled memory by
                 default.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

> Stability: 0 - Deprecated: Use [`Buffer.alloc()`][] instead (also see
> [`Buffer.allocUnsafe()`][]).

* `size` {integer} The desired length of the new `Buffer`.

See [`Buffer.alloc()`][] and [`Buffer.allocUnsafe()`][]. This variant of the
constructor is equivalent to [`Buffer.alloc()`][].

### `new Buffer(string[, encoding])`
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

> Stability: 0 - Deprecated:
> Use [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] instead.

* `string` {string} String to encode.
* `encoding` {string} The encoding of `string`. **Default:** `'utf8'`.

See [`Buffer.from(string[, encoding])`][`Buffer.from(string)`].

## `buffer` module APIs

While, the `Buffer` object is available as a global, there are additional
`Buffer`-related APIs that are available only via the `buffer` module
accessed using `require('buffer')`.

### `buffer.INSPECT_MAX_BYTES`
<!-- YAML
added: v0.5.4
-->

* {integer} **Default:** `50`

Returns the maximum number of bytes that will be returned when
`buf.inspect()` is called. This can be overridden by user modules. See
[`util.inspect()`][] for more details on `buf.inspect()` behavior.

### `buffer.kMaxLength`
<!-- YAML
added: v3.0.0
-->

* {integer} The largest size allowed for a single `Buffer` instance.

An alias for [`buffer.constants.MAX_LENGTH`][].

### `buffer.transcode(source, fromEnc, toEnc)`
<!-- YAML
added: v7.1.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `source` parameter can now be a `Uint8Array`.
-->

* `source` {Buffer|Uint8Array} A `Buffer` or `Uint8Array` instance.
* `fromEnc` {string} The current encoding.
* `toEnc` {string} To target encoding.
* Returns: {Buffer}

Re-encodes the given `Buffer` or `Uint8Array` instance from one character
encoding to another. Returns a new `Buffer` instance.

Throws if the `fromEnc` or `toEnc` specify invalid character encodings or if
conversion from `fromEnc` to `toEnc` is not permitted.

Encodings supported by `buffer.transcode()` are: `'ascii'`, `'utf8'`,
`'utf16le'`, `'ucs2'`, `'latin1'`, and `'binary'`.

The transcoding process will use substitution characters if a given byte
sequence cannot be adequately represented in the target encoding. For instance:

```js
const buffer = require('buffer');

const newBuf = buffer.transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
```

Because the Euro (`€`) sign is not representable in US-ASCII, it is replaced
with `?` in the transcoded `Buffer`.

### Class: `SlowBuffer`
<!-- YAML
deprecated: v6.0.0
-->

> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`][] instead.

See [`Buffer.allocUnsafeSlow()`][]. This was never a class in the sense that
the constructor always returned a `Buffer` instance, rather than a `SlowBuffer`
instance.

#### `new SlowBuffer(size)`
<!-- YAML
deprecated: v6.0.0
-->

> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`][] instead.

* `size` {integer} The desired length of the new `SlowBuffer`.

See [`Buffer.allocUnsafeSlow()`][].

### Buffer constants
<!-- YAML
added: v8.2.0
-->

#### `buffer.constants.MAX_LENGTH`
<!-- YAML
added: v8.2.0
-->

* {integer} The largest size allowed for a single `Buffer` instance.

On 32-bit architectures, this value currently is `(2^30)-1` (~1GB).
On 64-bit architectures, this value currently is `(2^31)-1` (~2GB).

This value is also available as [`buffer.kMaxLength`][].

#### `buffer.constants.MAX_STRING_LENGTH`
<!-- YAML
added: v8.2.0
-->

* {integer} The largest length allowed for a single `string` instance.

Represents the largest `length` that a `string` primitive can have, counted
in UTF-16 code units.

This value may depend on the JS engine that is being used.

## `Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()`

In versions of Node.js prior to 6.0.0, `Buffer` instances were created using the
`Buffer` constructor function, which allocates the returned `Buffer`
differently based on what arguments are provided:

* Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`)
  allocates a new `Buffer` object of the specified size. Prior to Node.js 8.0.0,
  the memory allocated for such `Buffer` instances is *not* initialized and
  *can contain sensitive data*. Such `Buffer` instances *must* be subsequently
  initialized by using either [`buf.fill(0)`][`buf.fill()`] or by writing to the
  entire `Buffer` before reading data from the `Buffer`.
  While this behavior is *intentional* to improve performance,
  development experience has demonstrated that a more explicit distinction is
  required between creating a fast-but-uninitialized `Buffer` versus creating a
  slower-but-safer `Buffer`. Since Node.js 8.0.0, `Buffer(num)` and `new
  Buffer(num)` return a `Buffer` with initialized memory.
* Passing a string, array, or `Buffer` as the first argument copies the
  passed object's data into the `Buffer`.
* Passing an [`ArrayBuffer`][] or a [`SharedArrayBuffer`][] returns a `Buffer`
  that shares allocated memory with the given array buffer.

Because the behavior of `new Buffer()` is different depending on the type of the
first argument, security and reliability issues can be inadvertently introduced
into applications when argument validation or `Buffer` initialization is not
performed.

For example, if an attacker can cause an application to receive a number where
a string is expected, the application may call `new Buffer(100)`
instead of `new Buffer("100")`, leading it to allocate a 100 byte buffer instead
of allocating a 3 byte buffer with content `"100"`. This is commonly possible
using JSON API calls. Since JSON distinguishes between numeric and string types,
it allows injection of numbers where a naively written application that does not
validate its input sufficiently might expect to always receive a string.
Before Node.js 8.0.0, the 100 byte buffer might contain
arbitrary pre-existing in-memory data, so may be used to expose in-memory
secrets to a remote attacker. Since Node.js 8.0.0, exposure of memory cannot
occur because the data is zero-filled. However, other attacks are still
possible, such as causing very large buffers to be allocated by the server,
leading to performance degradation or crashing on memory exhaustion.

To make the creation of `Buffer` instances more reliable and less error-prone,
the various forms of the `new Buffer()` constructor have been **deprecated**
and replaced by separate `Buffer.from()`, [`Buffer.alloc()`][], and
[`Buffer.allocUnsafe()`][] methods.

*Developers should migrate all existing uses of the `new Buffer()` constructors
to one of these new APIs.*

* [`Buffer.from(array)`][] returns a new `Buffer` that *contains a copy* of the
  provided octets.
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`]
  returns a new `Buffer` that *shares the same allocated memory* as the given
  [`ArrayBuffer`][].
* [`Buffer.from(buffer)`][] returns a new `Buffer` that *contains a copy* of the
  contents of the given `Buffer`.
* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] returns a new
  `Buffer` that *contains a copy* of the provided string.
* [`Buffer.alloc(size[, fill[, encoding]])`][`Buffer.alloc()`] returns a new
  initialized `Buffer` of the specified size. This method is slower than
  [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] but guarantees that newly
  created `Buffer` instances never contain old data that is potentially
  sensitive. A `TypeError` will be thrown if `size` is not a number.
* [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] and
  [`Buffer.allocUnsafeSlow(size)`][`Buffer.allocUnsafeSlow()`] each return a
  new uninitialized `Buffer` of the specified `size`. Because the `Buffer` is
  uninitialized, the allocated segment of memory might contain old data that is
  potentially sensitive.

`Buffer` instances returned by [`Buffer.allocUnsafe()`][] and
[`Buffer.from(array)`][] *may* be allocated off a shared internal memory pool
if `size` is less than or equal to half [`Buffer.poolSize`][]. Instances
returned by [`Buffer.allocUnsafeSlow()`][] *never* use the shared internal
memory pool.

### The `--zero-fill-buffers` command line option
<!-- YAML
added: v5.10.0
-->

Node.js can be started using the `--zero-fill-buffers` command line option to
cause all newly-allocated `Buffer` instances to be zero-filled upon creation by
default. Without the option, buffers created with [`Buffer.allocUnsafe()`][],
[`Buffer.allocUnsafeSlow()`][], and `new SlowBuffer(size)` are not zero-filled.
Use of this flag can have a measurable negative impact on performance. Use the
`--zero-fill-buffers` option only when necessary to enforce that newly allocated
`Buffer` instances cannot contain old data that is potentially sensitive.

```console
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
```

### What makes `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()` "unsafe"?

When calling [`Buffer.allocUnsafe()`][] and [`Buffer.allocUnsafeSlow()`][], the
segment of allocated memory is *uninitialized* (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a `Buffer`
created by [`Buffer.allocUnsafe()`][] without *completely* overwriting the
memory can allow this old data to be leaked when the `Buffer` memory is read.

While there are clear performance advantages to using
[`Buffer.allocUnsafe()`][], extra care *must* be taken in order to avoid
introducing security vulnerabilities into an application.

[RFC 4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
[WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/
[`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
[`Buffer.alloc()`]: #buffer_static_method_buffer_alloc_size_fill_encoding
[`Buffer.allocUnsafe()`]: #buffer_static_method_buffer_allocunsafe_size
[`Buffer.allocUnsafeSlow()`]: #buffer_static_method_buffer_allocunsafeslow_size
[`Buffer.from(array)`]: #buffer_static_method_buffer_from_array
[`Buffer.from(arrayBuf)`]: #buffer_static_method_buffer_from_arraybuffer_byteoffset_length
[`Buffer.from(buffer)`]: #buffer_static_method_buffer_from_buffer
[`Buffer.from(string)`]: #buffer_static_method_buffer_from_string_encoding
[`Buffer.poolSize`]: #buffer_class_property_buffer_poolsize
[`DataView`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView
[`ERR_INVALID_BUFFER_SIZE`]: errors.html#ERR_INVALID_BUFFER_SIZE
[`ERR_INVALID_OPT_VALUE`]: errors.html#ERR_INVALID_OPT_VALUE
[`ERR_OUT_OF_RANGE`]: errors.html#ERR_OUT_OF_RANGE
[`JSON.stringify()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
[`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
[`String#indexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
[`String#lastIndexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
[`String.prototype.length`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length
[`TypedArray.from()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from
[`TypedArray#set()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/set
[`TypedArray#slice()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice
[`TypedArray#subarray()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/subarray
[`TypedArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
[`buf.buffer`]: #buffer_buf_buffer
[`buf.compare()`]: #buffer_buf_compare_target_targetstart_targetend_sourcestart_sourceend
[`buf.entries()`]: #buffer_buf_entries
[`buf.fill()`]: #buffer_buf_fill_value_offset_end_encoding
[`buf.indexOf()`]: #buffer_buf_indexof_value_byteoffset_encoding
[`buf.keys()`]: #buffer_buf_keys
[`buf.length`]: #buffer_buf_length
[`buf.slice()`]: #buffer_buf_slice_start_end
[`buf.toString()`]: #buffer_buf_tostring_encoding_start_end
[`buf.values()`]: #buffer_buf_values
[`buffer.constants.MAX_LENGTH`]: #buffer_buffer_constants_max_length
[`buffer.constants.MAX_STRING_LENGTH`]: #buffer_buffer_constants_max_string_length
[`buffer.kMaxLength`]: #buffer_buffer_kmaxlength
[`util.inspect()`]: util.html#util_util_inspect_object_options
[ASCII]: https://en.wikipedia.org/wiki/ASCII
[Base64]: https://en.wikipedia.org/wiki/Base64
[ISO-8859-1]: https://en.wikipedia.org/wiki/ISO-8859-1
[UTF-8]: https://en.wikipedia.org/wiki/UTF-8
[UTF-16]: https://en.wikipedia.org/wiki/UTF-16
[binary strings]: https://developer.mozilla.org/en-US/docs/Web/API/DOMString/Binary
[endianness]: https://en.wikipedia.org/wiki/Endianness
[iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols
